GB2027998A - An electric time switch - Google Patents

Abstract

An analogue time indicator 6,7, is combined with an adjusting device 29 for an alternatively usable long-term programme and a short-term programme, e.g. a weekly programme and a daily programme, and a common time drive, there being provided one disc- or ring-shaped programme carrier 15 which can be equipped with detachable tappets 19, each of which actuates a contact switching system (not shown), and which is provided, for example, with a 7-day scale and/or a 24-hour scale and which is drivable in accordance with its desired programme duration, for example at one rotation per week or one rotation per day. As shown, motor 5 drives hour and minute indicators 6 and 7 via gearing 4, and carrier 15 by 1:1 gearing 35,13 or by 7:1 gearing 36,14, selected by the axial position of shaft 33 which is adjustable by turning cam 41 by screw-driver rotation of shaft 39. Change-over at suitable times is ensured by a pin 37 which has to pass through a slot 38 in plate 1. <IMAGE>

Description

SPECIFICATION An electric switching clock The invention relates to an electic switching clock comprising an analogue time indicator and/or a fine adjusting device for optionally usable long-term and short-term programmes, e.g. a weekly programme and a daily programme, and a joint time drive, there being provided for programming respectively one disc- or ring-shaped programme carrier which can be equipped with switch tabs, which are insertable in a form-locked manner and each of which actuates a contact switching system, and which is provided, for example, with a 7-day scale and/or a 24-hour scale and which is drivable in accordance with its maximum programme duration at, for example, one rotation per week or one rotation per day.

Such switching clocks are mainly used for controlling heating systems in conjunction with thermostatic regulators and essentially serve for switching the thermostatic control from a higher room temperature by day to a lower room temperature by night and vice versa. There is to be provided the possibility of optionally choosing for the control the weekly or 7-day programme or else the daily or 24-hour programme, depending on whether a different programme is to be effective on specific weekdays or whether all weekdays have the same daily programme. In general, there is required for such switching clocks a high setting accuracy for the weekly programme, too, as well as a high switching resolution, i.e. short, minimal switching intervals.Furthermore, there are preferred programme carriers comprising switch tabs which are insertable in a form-locked manner and which actuate the contact switching system.

There already exist switching clocks which are provided with two switching or programme discs which are arranged side by side or coaxially one above the other. These switching clocks necessitate a high expenditure because two complete contact systems have to be provided for each switching disc.

While the juxtaposed switching discs have the additional disadvantage of a large space requirement, the switching clocks provided with two switching discs which are coaxially arranged one above the other have the further disadvantage that the lower disc is less accessible and thus more difficult to programme, unless the upper programme disc is removable for programming the lower programme disc, as is the case with a known switching clock of this kind.

There is also already known a switching clock which is equipped with two interchangeable programme carriers, namely a daily programme disc and a weekly programme disc, which can be optionally placed on the switching shaft (Advertising pamphlet Landis & Gyr G 24 66, RVP), but has no analogue time indicator and which therefore makes it difficult to attain an accurate time setting of the weekly programme disc, in particular.

The task underlying the invention is to provide an electric switching clock with an analogue time indicator of the kind mentioned at the beginning which ensures an equally high setting accuracy for both programmes with the aid of the manually adjustable analogue time indicator, which is preferably arranged so as to be concentric with a programme carrier, and which allows the change-over from the short-term programme to the long-term programme and vice versa to be effected in a simple manner and free of time errors.

According to the invention, this task is solved in that one and the same programme carrier is provided for both programmes, namely the long-term or weekly programme and the short-term or daily programme, and in that the programme carrier is fixedly connected to the switching clock mechanism, is associated with one and the same contact system and is provided with a switch-over gearing which allows its speed of, for example, one rotation per week to be switched to, for example, one rotation per day and vice versa.

Such a switching clock has the great advantage that a change-over from the weekly programme to the daily programme or vice versa can be effected by a simple switch-over of the drive and by a corresponding new programming of the programme carrier, i.e. a new insertion of the switch tabs, without any need to remove the programme carrier itself from the switching clock mechanism and to replace it by a different one. By this means, the kinematic connection between the time indicator and the programme carrier, which is unchangeable as such, is maintained in any event, time errors in the switching programme thus being reliably avoided.

Because of the given relations between the daily programme scale and the weekly programme scale, which are arranged on the same programme carrier, as well as the time indicator, error-free switch-overs from the daily programme to the weekly programme or vice versa can be carried out only at specific points in time or in specific positions of the time indicator and the programme carrier.

In order to ensure that these switch-overs can only be effected at the mentioned points in time or in the specific positions of the daytime indicator and the programme carrier, provision is made, in a further development of the invention, for the switch-over gearing to be provided with a switch prevention device which allows a switch-over to be effected only in specific time positions of the programme carrier and the analogue time indicator respectively.

In a further development of the invention, provision may be made for the programme carrier, which is provided with an integrally formed plug-in facility serving for the form-locked reception of the switch tabs to be provided with a 7-day scale and a 24-hour scale, both of which are printed thereon so as to be concentric with the plug-in facility. However, this constructional form, which is the simplest in principle, has the slight disadvantage that the scale which lies on the smaller diameter cannot be directly adjacent to the form-locking plug-in provided in the form of axial grooves or axial bores if these are provided on the outer circumference of the programme carrier, which is however not absolutely necessary.

In another constructional form of the switching clock, provision is made for the programme carrier provided with an integrally formed plug-in facility serving forthe form-locked reception of switch tabs to have only one scale printed thereon, namely either the 7-day scale or the 24-hour scale, and for the respective other scale to be printed on a ring which can be placed on the programme carrier in specific scale-related positions and can be removed therefrom in any position.

This constructional form has the advantage that both scales, i.e. the 7-day scale and the 24-hour scale, can be mounted on the same diameter so as to directly adjoin the plug-in facility on the circumference of the programme carrier, which contributes substantially to facilitating an exact programming because the scale division lines thus extend directly up to the switch tabs set.

In a further constructional form of the invention, provision is made for the ring which can be placed on the programme carrier in specific scale-related positions to have the 7-day scale printed on one side and the 24-hour scale on the other side.

By this means, the advantage is attained that the ring can stay on the programme carrier in any programme and only has to be turned when the programme is changed, i.e. there is no need to remove the ring from the switching clock in any of the possible programmes so that there is no risk of it being lost. In this connection, it is advantageous if the programme carrier is additionally provided with the 7-day scale because by this means the scalerelated positioning of the ring on the programme carrier is substantially facilitated when the programme is switched from the daily programme to the weekly programme, namely in that all that is needed is to bring the 7-day scale printed on the top side of the ring into coincidence with the 7-day scale also printed on the top side of the programme carrier.

In order to facilitate the respective superimposition of the ring provided with scales on one or both sides on the programme carrier with respect to the scale-related positions, it is advantageous if the programme carrier has a total of 7 plug-in recesses in the form of grooves, holes or the like which are accessible from the top thereof and are provided at equal angular distances from one another and each lie on the 12-o'clock mark of the individual weekdays of the 7-day scale and if the ring, which has at least one scale printed thereon, is provided with at least one plug-in element in the form of a pin or the like fitting into the grooves or ho les or the like, which element lies on the 12-o'clock mark on a 24-hour scale and/or on the 12-o'clock mark of an optional weekday of the 7-day scale.

The advantages attained thereby will be explained in more detail in the following description of exam ples.

The ring itself may be provided with plug-in elements which project from one or both sides and are arranged accordingly.

Finally, there furthermore exists the advantageous possibility of the plug-in facilities serving for the form-locked reception of the switch tabs being integrally formed with the ring, which is provided with a scale on one or both sides and which can be placed on the programme carrier, rather than with the programme carrier, and in this connection it is possible to design these plug-in facilities in such a way that plug-in tabs can be inserted from both sides or from one side only.

If the plug-in facilities are provided on the ring in duplicate, so that there is available respectively a plug-in facility which is adapted divisionwise to the 7-day scale and a plug-in facility which is adapted to the 24-hour scale, then a maximum setting accuracy is given because it is then possible to associate on both scales a groove, bore or the like, serving as the plug-in facility, with each scale division line.

The invention will now be explained hereinafter in several exemplified embodiments with reference to the drawings, in which: Figure 1 shows a partial section through a switching clock provided with a programme carrier and a switch-over gearing, Figure 2 shows another constructional form of the switching clock shown in Figure 1, Figure 3 shows a further constructional form of the switching clock shown in Figure 1, Figures 4, 5 and 6 show the switch-over gearing with the programme carrier in different switching positions, Figure 7 shows the switch-over mechanism for the switch-over gearing, Figure 8 shows a graduated ring in a top view, Figure 9 shows a graduated ring of Figure 8 in section along the line of intersection IX-IX, Figure 10 shows a programme carrier with an analogue time indicator in a top view, Figure 7 1 shows another programme carrier with an analogue time indicator in a top view, Figure 12 shows a simplified linear representation of the two programme scales for the 7-day programme and the 24-hour programme, and Figure 13 shows, in a linear representation, a scale section of one day of the 7-day scale and of a corresponding length of the 24-hour scale in relation to the plug-in tab grooves of the programme carrier, The switching clock, with the aid of which the invention will hereinafter be explained by way of example, comprises a switching mechanism which is substantially constructed on two mechanism plates 1 and 2, as can be seen in Figure 1. The mechanism plates 1 and 2 are connected together by pillars 3. Located between them is the gear mechanism 4 which is driven by a synchronous motor 5 and which drives the indicator discs 6 and 7 of the analogue time indicator. The minute tube 8, on which the minute indicator disc 6 is fastened, and the hour tube, on which the hour indicator disc 7 is fastened, are mounted in a fixed bearing bush 10 so as to lie one within the other and to be each rotatable by itself. The bearing bush 10 is fixedly riveted into the mechanism plate 1. Its axis forms the centre of the switching clock. On a cylindrical lug 11 of the bearing bush 10, there is rotatably mounted a circular disc 15 which is provided with a hub 12, a gear 13 and a gear 14 and which serves as the programme carrier. The disc 15 has in the centre a circular cylindrical depression 16, in which there are accommodated at the bottom a dial face 17 and the two indicator discs 6 and 7 of the analogue time indicator. The dial face 17 is stationarily secured on an upper lug 18 of the bearing bush 10. The disc 15 has on its circumference plug-in facilities for insertable switch tabs 19, which plug-in facilities take the form of an annular groove 20, which is open at the top, and a specific number of axial grooves 21 in the shape of profiled triangles, this number of axial grooves being as a rule either 7 x 24 = 168 or 7 x 48 = 336, depending on the required switching resolution.The annular grooves 22 and 22' provided on the underside and in the recess of the disc 15 are only provided for reasons of saving material and of injecting-moulding technique, since the disc 15 is made of a plastics material by the injection moulding method in series production.

The switch tabs 19 are each provided with a switching nose 23, by means of which they actuate, during the rotation of the disc 15 at specific points in time, a contact switching system (not shown) which serves for controlling circuits of any type and in the present case serves for controlling a thermostatic regulator of a heating system.

The minute indicator disc 6 which, like the hour indicator disc, consists of a transparent plastics material, comprises a centric turning knob 24, with which a time setting can be manually effected on the analogue time indicator, as is as a rule the case with analogue clocks.

On the upper ring surface 25 of the disc 15, which surface surrounds the recess 16, there is superimposed a flat ring 26 which is shown as a single component in Figure 8 and on which there is printed, at least on the ring surface that is located on top in Figure 1,a 24-hour scale. For positioning and fixing the ring 26, the latter is provided with pins 27 which can be inserted into plug-in bores 28 in a fitting and possibly detented manner.Irrespective of whether the ring 26 is only provided with a 24-hour scale on the upper ring surface shown in Figure 1 or also with a 7-day scale on the lower side thereof, as will be demonstrated later by further examples, in the present examplified embodiment shown in Figure 10, there is printed on the ring surface 25 of the disc 15 a 7-day scale, whose smallest division corresponds to an interval of2 hours. Only for reasons of drawing technique, the divisions of the axial grooves 21 shown in Figures 10 and 11 are designed for a 2-hour interval; however, in reality, at least 168 axial grooves 21 are provided on the circumference of the disc 15 so that, as shown in Figure 13, the minimum interval of the 7-day programme is not two hours but only one hour.

The drive of the disc 15 is effected by a switch-over gearing 29 which is also driven from the synchronous motor 5 through double back gears 30 and a pinion 31, which communicates with the minute tube 8 through a shaft 32. The switch-over gearing consists of a shaft 33 which is mounted in the mechanism plates 1 and 2 so as to be axially parallel to the bearing bush 10 and so as to be axially displaceable and which communicates kinematically with the back gears 30 through a gear 34 secured thereon and which is provided, at its upper end located above the mechanism plate 1, with a gear 35 and a pinion 36, which are connected thereto so as to be secured against rotation.The shaft 33 furthermore comprises a transverse pin 37 which is so arranged that in the upper end position of the shaft 33 it lies above the mechanism plate 1 and in the lower end position thereof beneath the mechanism plate 1. For the passage of this transverse pin 37, the mechanism plate 1 is provided with a radial slot 38, through which the transverse pin 37 can slide in a fitting manner when the shaft is in the appropriate angular position. The transverse pin 37 serves as a switch prevention device which is to ensure that the switching-over of the switch-over gearing 29 can only take place in a specific angular position of the shaft 33 and thus only at specific points of daytime.

In the switch positions shown in Figures 1,2 and 3, the shaft 33 is in its upper end position and the pinion 36 is in engagement with the gear 14 of the disc 15. The duration of the weekly programme is set at this engagement, which means that the disc 15 rotates through 360" once in seven days. In the lower end position of the shaft 33, the gear 35 is in engagement with the gear 13 of the disc 15. When this is the case, the disc 15 is driven at a rotational speed of one rotation per 24 hours. The speed ratio between the gears 35 and 13 is 1:1. The speed reducing ratio between the pinion 16 and the gear 14 is 7:1. This means that the shaft 33, with the gear 35 and the pinion 36, is driven at one rotation per 24 hours.

For the actuation of the switch-over gearing 29 or for the axial displacement of the shaft 33, there is provided on a shaft 39, which is rotatably mounted in the mechanism plates 1 and 2, a lever arm 40 comprising an axial control arm 41, on which there rests in a spring-loaded manner a tappet 42 which is guided so as to be axially displaceable in a bore 43 of the shaft 33. At the lower end of the tappet, there is secured a disc 44, on which there rests a compression spring 45, whose other end is supported on a disc 46 which is secured to the lower end of the shaft 33.Between the disc 46 and the lower mechanism plate 2, there is arranged a compression spring 47 which has the task of pressing the shaft 33 downwards when the cam disc 41 is shifted accordingly and of thereby effecting the switch-over from the weekly programme to the daily programme. the spring 45, which is considerably stronger than the spring 47, is only intended for avoiding damage if obstructions of any kind should occur during an initiated switch-over process from the daily programme to the weekly programme, i.e. when the shaft 33 is to be moved from its lower position ot its upper position.

The rotary movement of the shaft 39 with the control cam 41 is limited by two transverse pins 49 and 50 which strike against a nipple 48 in the extreme positions of the control cam 41. As can be seen best in Figure 7, the shaft 39 comprises above the mechanism plate 1 a slotted head 51 with an indicator 52, so that the shaft 39 can be rotated by means of a screw turning tool from the line mark "week" provided on the mechanism plate top to the line mark "day" and vice versa.

In Figures 4, 5 and 6, the switch-over gearing 29 is shown in perspective in three different functional positions. While in Figure 4, the two gears 13 and 35 are in engagement with each other and the shaft 33 is in its lowest position, the swtich-over operation is shown in Figure 5 in such a way that it is discernible that over a certain distance of movement of the shaft 33 both transmissions are simultaneously in engagement, i.e. that there engage simultaneously the gear 35 with the gear 13 and the pinion 36 with the gear 14. This is necessary so as to avoid time errors during the switch-over through incorrect engagements. In Figure 6, the pinion 36 is in engagement with the gear 14, while the gear 35 has completely released the gear 13.The fact that only a bush 33' with the gear 35 and the pinion 36 are shown in an axially displaceable manner in Figures 4, 5 and 6, instead of the shaft 33, is of minor importance and only indicates a possibility of practical realisation other than that shown in Figures 1, 2 and 3. Another difference between the constructional form of Figures 4,5 and 6 and that of Figures 1,2 and 3 is to be seen in the fact that the bush 33', on which the gear 35 and the pinion 36 are fastened, comprises, instead of the transverse pin with which the shaft 33 is equipped, two diametrically opposite radial locking fingers 53 and 54 and, accordingly, the mechanism plate 1 comprises two recesses 55 and 56 which lie also diametrically opposite to each other and are adapted in their cross section to the locking fingers 53 and 54.Functionally, the effect of this difference is that instead of being effected after every full rotation of the shaft 33, as in the constructional form of Figure 1, a switch-over of the switch-over gearing 29 can be effected after every half-rotation of the bush 33'.The ring 26' shown in Figures 8 and 9 has printed on one side a 24-hour scale, which is visible in Figure 8 at the top, and on the other side a 7-day scale which corresponds exactly to that which is printed on the disc 15 shown in a top view in Figure 10. The ring 26' is provided, at the 12-hour mark, with a first plug-in pin 57, which projects from both sides of the ring, as well as with two further plug-in pins 58 and 59, which also project from both sides and which are each at an angular distance from the 24-hour mark, which lies diametrically opposite to the 12-hour mark, of a/2, the angle a being 1/7 of 360".Expressed in other words, the angular distances of the two plug-in pins 58 and 59 from the plug-in pin 57 each carry, as viewed in opposite directions of rotation, 3/7 of a full circle. Due to the fact that the plug-in pins 57, 58 and 59 project from the ring 26' on both sides, it is possible to superimpose this latter on the disc 15, serving as the programme carrier, with one side or scale or the other pointing to the top.Since in the daily or 24-hour programme it is irrelevant, on the one hand, with which day section of the 7-day scale the 12-hour mark of the 24-hour scale on the ring 26' or 26 is aligned, but it is necessary, on the other hand, that the 12-hour mark of the 24-hour scale should agree with the 12-hour mark of the respective day section of the 7-day scale, there are provided in the disc 15 at all the 12-hour marks of the 7-day scale plug-in holes 28, into which the plug-in pins 57, 58 and 59 fit.

The fact a time-error-free switch-over from the daily programme to the weekly programme and vice versa can only take place at specific times is discernible from Figure 12, in which the two scales the 7-day scale on the left-hand side, the 24- scale on the right-hand side - are linearly shown, namely in that the 12-hour mark of the 24-hour scale only agrees with the 12-hour mark of the Thursday section of the 7-day scale and for the rest only the start and end marks coinciding in a circular scale.

In the constructional form shown in Figure 11, where the disc 15 has printed on its ring surface 25 both the 24-hour scale and the 7-day scale, which are concentric with each other, and where the ring 26 or 26' is unnecessary, the switch-over from the weekly programme to the daily programme, i.e. the switchover of the switch-over gearing 29 from the functional position shown in Figures 1 and 6 to the functional position shown in Figure 4, can only be effected twice per week, namely on Sunday at 24 hours and on Thursday at 12 hours.To this end, it of course not necessary to carry out these switch-overs really at noon on Thursday or during the night on Sunday, but these switch-over times can be manually set for the purpose of the switch-over by the appropriate rotation of the disc by means of the minute disc, which is provided with a turning knob 24, and can be reset to the correct time of the day or week following the switch-over.

By contrast, the switch-over from the daily programme to the weekly programme, i.e. from the gearing position of Figure 4 to the gearing position shown in Figures 1 and 6, can be effected attwo points in time per day, namely at 12 hours and at 24 hours. That is to say, all that is necessary for the switch-over is to set the time to 12 hours or 24 hours by way of the appropriate rotation of the minute indicator disc 6. However, a precondition for these two possible switch-over times is that there are provided in the mechanism plate 1 two recesses 55 and 56 and not only a single slot 38 as in the constructional form of Figure 1.

If, however, as in the exemplified embodiment of Figures 8,9 and 10, the programme carrier is provided with a graduated ring 26 or 26', which comprises the 24-hour scale on one side and the 7-day scale on the other side, the switch-over from the weekly programme to the daily programme can be effected in the 12-hours position of the analogue time indicator, i.e. in the position of 12 hours or 24 hours. It is obvious that in this connection the ring with the two scales also has to be turned so that the 24-hour scale will lie on top instead of the 7-day scale.

The switch-over from the daily programme (one rotation of the disc per day) to the weekly programme (one rotation of the disc per week) can also always be effected when the analogue time indicator points to 12 hours. The ring 26' must then be placed on the disc 15 (Figure 10) so that the 7-day scale of the ring 26' coincides with the 7-day scale of the disc 15.

While, in the constructional forms described so far, the plug-in facilities, i.e. the grooves 21 for the switch tabs 19, are integrally connected to the disc 15 serving as the programme carrier and there have to be accepted, as a result, division intervals of these axial grooves 21 which do not exactly agree with the scale divisions of the 24-hour scale, which results however only in negligibly small setting errors of the order of 1 - 2 minutes, it is also possible to provide the plug-in facilities for the switch tabs 19 integrally on a graduated ring 26/1 or 26/2, on which scales are printed on one or both sides, as shown in Figure 2 or Figure 3. In the constructional form of Figure 2, the annular groove 20, which is integrally formed with the disc 15 in the constructional form of Figure 1, and the axial grooves 21 are integrally formed with the graduated ring 26/1.The disc 15' therefore has a smooth cylindrical external surface 15". In this case, which is however less favourable, it would be necessary to provide two graduated rings 26/1, of which one is provided with the 7-day scale and the other with the 24-hour scale. The division intervals of the axial grooves 21 could then be different on the two graduated rings 26/1, namely in such a way that they agree respectively with the division lines of the printed-on scales so as to allow the insertable tabs to be set in a manner that is accsurate scalewise.

By contrast, in the constructional form of Figure 3, the graduated ring 26/2 can be used on both sides and, like the ring 26', is provided with a single insertable pin 57 which projects from both sides of the ring. Integrally formed with the circumference of the graduated ring 26/2, on which a scale is respectively printed on both ring surfaces, i.e. at the top and at the bottom, namely the 24-hour scale on one side and the 7-day scale on the other side, are two plug-in facilities for switch tabs 19', each facility consisting of an annular groove of equal cross section at the top and bottom and axial grooves 21 or 21' having different division intervals which are adapted to the respective scale associated therewith.

The manipulation of this graduated ring 26/2 is the same as that of the ring 26' which has both sides imprinted, the graduated ring 26/2 having however the advantage that the insertable tabs 19' can be accurately inserted in relation to the scale. In accordance with the modified shape of the graduated ring 26/2 in relation to the graduated ring 26' and the graduated ring 26/1,the cross-sectional shape of the disc 15/1, which serves in this case as the programme carrier, has also been slighly modified in relation to the cross-sectional shape of the disc 15' of Figure 2 and 15 of Figure 1. All the other parts of Figures 2 and 3 equal those of Figure 1 and are provided with the corresponding reference symbols.The annular grooves 20 and 20', which form part of the two plug-in facilities for the switch tabs 19', are expediently somewhat less deep than the annular groove 20 in the constructional forms of Figures 1 and 2.

It is understood that devices other than those given in the exemplified embodiment can be used as the switch-over gearing. What is however important in any event is that the switch prevention device should be effective, if possible, directly on the switching shaft, i.e. on the driving shaft (33 or 33') which can be brought into engagement with the gear 13 sor 14, if switching time errors during the switch-over, i.e. incorrect tooth engagements between the gears 13 and 14, on the one hand, and the gear 35 and the pinion 36, on the other hand, are to be avoided.

In order to attain an even greater reliability in this respect, it is recommended to design the slot 38 or the recesses 55 and 56 on both sides with funnel-like catching devices and/or the pin 37 as well as the projections 53 and 54 in a wedge-like manner at the top and bottom, so that they inevitably reach, during the switch-over operation, the exactly correct angular positions guaranteeing the only new engagement that is correct, i.e. faultless.

Claims (14)

1. An electric switching clock comprising an analogue time indicator and/or a fine adjusting device for an optionally usable long-term programme and a short-term programme, e.g. a weekly programme and a daily programme, and a joint time drive, there being provided for programming respectively one disc- or ring-shaped programme carrier which can be equipped with switch tabs, which are insertable in a form-locked manner and each of which actuates a contact switching system, and which is provided, for example, with a 7-day scale and/or a 24-hour scale and which is drivable in accordance with its maximum programme duration, for example at one rotation per week or one rotation per day, wherein for both programmes, namely the long-term or weekly programme and the short-term or daily programme, one and the same programmer carrier is fixedly connected to the switching clock mechanism, is associated with one and the same contact system and is provided with a switch-over gearing, through which its rotational speed can be switched over from e.g. one rotation perweekto e.g.

one rotation per day and vice versa.

2. A switching clock as claimed in Claim 1, wherein the switch-over gearing (29) is provided with a switch prevention device which allows a switch-over to take place only at specific time settings of the programme carrier or the analogue time indicator.

3. A switching clock as claimed in Claim 1 or Claim 2, wherein the programme carrier provided with an integrally formed plug-in facility serving for the form-locked reception of the switch tabs is provided with a 7-day scale and a 24-hour scale, both of which are printed on so as to be concentric with the plug-in facility.

4. A switching clock as claimed in Claim 1 or Claim 2, wherein the programme carrier provided with an integrally formed plug-in facility serving for the form-locked reception of switch tabs has only one printed-on scale, namely either the 7-day scale or the 24-hour scale, and in that the respective other scale is printed on a ring which can be superimposed on the programme carrier in specific scale-related positions and can be removed therefrom in any position.

5. A switching clock as claimed in Claim 1,2 and 4, wherein the ring superimposable on the programme carrier in specific scale-related positions has the 7-day scale printed on one side and the 24-hour scale on the other side.

6. A switching clock as claimed in Claims 1,2 and 4 or 5, wherein the programme carrier is provided with altogether seven plug-in recesses in the form of grooves, holes or the like, which are accessible from the top thereof and which are provided at equal angular distances from one another and which lie respectively on the 12-hour mark of the individual weekdays of the 7-day scale, and in that the ring, on which at least one scale is printed, is provided with at least one insertable element in the form of a pin or the like fitting into the grooves or holes, which element lies on the 12-hour mark of the 24-hour scale and/or on the 12-hour mark of any weekday of the 7-day scale.

7. A switching clock as claimed in Claim 6, wherein in addition to the insertable element lying on the 12-hour mark of the 24-hour scale or on the 12-hour mark of the first day of the 7-day scale, the ring comprises two further insertable elements, whose angular distances from the first-mentioned insertable element is respectively 3/7 of the full circle.

8. A switching clock as claimed in Claims 6 and 7, wherein the insertable elements are provided on both sides of the ring,

9. A switching clock as claimed in Claims 1,2,6 and 7 or 8, wherein the plug-in facilities serving for the form-locked reception of the switch tabs are integrally formed with the ring rather than with the programme carrier, which ring is provided with a scale on one side or both sides and can be placed on the programme carrier.

10. A switching clock as claimed in Claim 9, wherein the ring is provided with two different plug-in facilities, whose axial grooves have different division intervals which are adapted to the respective scale associated therewith.

11. A switching clock as claimed in Claims 1 and 2, wherein the switch prevention device is effective on the shaft of the switch-over gearing which shaft can be alternately brought into engagement with one of the two gears secured on the disc.

12. A switching clock as claimed in Claims 1,2 and 11, wherein the switch prevention device consists of radial projections arranged on the shaft of the switch-over gearing and of lock-like gates, which are adapted to the respective length and width of the associated projections in a stationary frame part.

13. A switching clock as claimed in Claims 1,2, 11 and 12, wherein the gates are provided on both sides with funnel-like catching devices for the projections.

14. An electric switching clock substantially as described with reference to the accompanying drawings.